The Difference Between Physical and Mental Fatigue, Explained

Experts break down how to tell if you're physically exhausted or mentally drained — and how to get your energy levels back on track.

Tired woman laying in comfortable bed with feet hanging off next to a laptop
Photo: Stocksy

Start typing "Why am I…" in Google, and the search engine will auto-fill with the most popular query: "Why am I... so tired?"

Clearly, it's a question many people are asking themselves every day. In fact, one study found that nearly 40 percent of Americans wake up most days of the week feeling tired.

But when you can't focus in the middle of the workday or find yourself lying awake in bed for 20 extra minutes instead of going for a run, you might be wondering if physical exhaustion is actually to blame.

Turns out, it may not be. There are two completely different types of tiredness that can affect your day-to-day life: mental fatigue and physical fatigue, says Kevin Gilliland, Psy.D., a clinical psychologist and executive director of Innovation 360 in Dallas. They generally have different symptoms, but both can play into and affect each other.

Here's how to tell if you're physically exhausted or dealing with mental fatigue — and what to do about it. (

Causes and Symptoms of Physical Fatigue

The culprits behind physical exhaustion are typically either overtraining or lack of sleep. "Most people think of 'overtraining' as something that would only affect elite athletes, but that's not true," says Sheri Traxler, M.Ed., a certified health coach and exercise physiologist. "You can be a newbie to exercise and experience overtraining — especially if you're going from a sedentary lifestyle to training for a half marathon, for example."

Signs of overtraining include an increased resting heart rate, muscle aches that don't dissipate within 48 to 72 hours after a workout, headaches, and decreased appetite (as opposed to an increased appetite, which usually occurs with increased physical activity), according to Traxler. If you notice any of these symptoms of physical fatigue, take a couple days off for rest and recovery.

The other main reason is sleep deprivation, which is a much more common cause, says Traxler. "You may not be sleeping enough hours or your quality of sleep is poor," she explains.

Still tired even after you've been in bed for eight or more hours? That's a sign you're not sleeping well, says Traxler. Another clue: You wake up feeling rested after a "good" night's sleep, but then at 2 or 3 p.m., you hit a wall. (One side note: Hitting a lull at 2 or 3 p.m. is completely normal, due to your natural circadian rhythms, notes Traxler. Hitting a wall that makes you feel completely fatigued is not.)

Poor-quality sleep can be caused by a plethora of issues, including stress, hormones, and thyroid or adrenal problems, says Traxler. If you suspect you're not sleeping well, the next step is to see your primary care physician or endocrinologist. "Seek an M.D. who's also a naturopath or functional medicine expert, so they can take a look more deeply into your bloodwork, nutrition, and stress levels to figure out what's going on," suggests Traxler.

In the Ayurvedic tradition (the traditional, holistic Hindu system of medicine), physical exhaustion is known as a vata imbalance. "When vata rises, the body and mind become weak and exhaustion sets in," notes Caroline Klebl, Ph.D., a certified yoga teacher and an expert in Ayurveda. According to Ayurveda, this can arise from overactivity and lack of sleep, but also skipped meals, undereating, and overuse of stimulants, such as caffeine.

To overcome exhaustion the Ayurvedic way, it's important to sleep regular hours — approximately eight hours a day, preferably going to sleep by 10 or 11 p.m., says Klebl. "Eat regular and healthy meals, including fruits, vegetables, grains, and proteins, without eating too much or too little, and reduce or eliminate caffeine intake." So, basically, everything you've ever heard about eating healthy.

Causes and Symptoms of Mental Fatigue

Mental exhaustion is a very real thing as well, says Gilliland. Specifically, mental fatigue is defined as a failure to complete mental tasks that require self-motivation and internal cues, without any physical cause, which reduces your day-to-day efficiency, according to research published in Behavioral and Brain Functions. "A stressful day at work or working intensely on a project can exhaust our mental fuel for the day, leaving us feeling worn down," explains Gilliland.

When suffering from mental fatigue, you might have difficulty performing daily tasks or making routine decisions, feel irritable or short-tempered, become easily distracted or feel like you're "in a fog," or procrastinate on certain responsibilities, according to information published by the Children's Hospital of Philadelphia. It can also affect your sleep at night, as your mind can't "turn off," continuing the harmful cycle of poor sleep, explains Gilliland.

To get a clearer understanding of whether you're dealing with physical or mental fatigue, take this "test" from Traxler: Ask yourself if you'd feel energized if you were invited to do your favorite thing in the world right now — whether that's shopping or going out to dinner. "If even your favorite hobbies do not sound appealing, you're probably physically tired," says Traxler.

Having trouble with the hypotheticals? Another way to test whether you're physically or mentally exhausted is to create a small commitment and stick to it, suggests Traxler. "Make a minimal (five- to 10-minute) effort to do to whatever you're trying to do, whether it's a workout at the gym or cooking a healthy dinner at home."

If it's the gym, perhaps your minimum commitment is to simply put on your workout clothes or drive to the gym and check in. If you take that step but you're still exhausted and dreading the workout, don't do it. But chances are, if you're just feeling mentally — not physically — fatigued, you'll be able to rally and follow through with it. Once you've broken the inertia (you know: objects at rest stay at rest), you might feel more energized.

That, in fact, is the key for any sort of mental fatigue: Break the inertia. The same solution for mental fatigue applies when you're sitting at your desk, feeling your eyelids get heavier and heavier, during a dull Wednesday afternoon. In that instance, simply get up and move, says Traxler. "Stretch at your desk or in the copy room, or get out and walk around the block for 10 minutes," she says. "Getting a dose of sunshine is another great way to beat the afternoon slump."

In Ayurvedic tradition, mental fatigue may be a sign of a kapha imbalance, and it arises from inactivity or overeating, notes Klebl. The best way to reduce a kapha imbalance is, again, movement. Klebl recommends three to five hours of exercise per week. Plus, make sure not to oversleep, she notes. "Set an alarm in the morning and wake up to practice yoga or go for an early morning walk." Also, make sure you're eating lightly in the evening, as well as reducing your sugar intake and your consumption of oily foods and alcohol.

What to Do If You're Suffering Physical or Mental Fatigue

If you're regularly feeling mentally or physically worn down, take a look at these five usual suspects before heading to a doctor, says Gilliland. "Evaluate how you're doing in these five areas of your life, and then go to a doctor and run some tests," he says. "We tend to go in the opposite order, running to our doctor first without evaluating the root causes of our tiredness." Mentally run through this checklist first:

  • Sleep: Are you getting enough sleep? Experts recommend seven to nine hours.
  • Nutrition: How's your diet? Are you consuming a high amount of sugar or caffeine, which could mess with your sleep schedule? (Also consider these foods for better sleep.)
  • Exercise: Are you moving enough throughout the day? Sitting hunched over a desk all day and not taking some time for movement can cause a feeling of lethargy, explains Gilliland.
  • Stress: Stress isn't always a bad thing, but it can impact your energy levels and sleep and, in the long run, bring on mental fatigue. Make time for self-care and stress-reduction techniques.
  • People: Are people in your life bringing you down, or lifting you up? Are you spending enough time with loved ones? Isolation can make you feel mentally exhausted, even if you're a self-described introvert, says Gilliland.

It's sort of like that airplane oxygen mask metaphor: You have to take care of yourself and your body first before you can help anyone else. Similarly, when it comes to self-care, think of your mind as your phone, suggests Gilliland. "You charge your phone every night. Ask yourself: Are you re-charging yourself?" Just like you want your phone to be at 100 percent battery power when you wake up, you want your body and mind to be the same, he says. Take the time to recharge and replenish yourself each night, and you too will be functioning at 100 percent.

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